[Wien] Different Rmt's for atoms of one type

[Евгения Каблиман]

Maxim, perhaps, you are interesting in calculation of the formation
energies.
And therefore, I am personally not sure, how is then better (and correct) to
estimate this value when Fe atoms have different RMT's in one supercell.
As Laurence very well explained, when "you use different RMTs for the Fe in
effect you make them different".

2011/4/21 Laurence Marks <L-marks at northwestern.edu>

> An approximate explanation, but first a caveat: dealing with small
> RMT's in Wien2k is not completely trivial.
>
> In Wien2k you have two different basis sets, a radial grid + orbitals
> inside the RMT, plane waves outside. If you use different RMTs for the
> Fe in effect you make them different. For instance, try setting up a
> Fe cell with two different RMTs (i.e. a supercell), converge it then
> do aim. You will find that there has been a small charge transfer
> between the Fe's, which will go to zero as you increase RKMAX.
>
> For your problem, I would go beyond setrmt (which is OK, but not
> always optimal) and use a smaller RMT for the C (maybe 1.3) and
> increase that for the Fe. You will have to do this by hand. Be careful
> about going too small with the C as if you do you will lose core
> charge (although .lcore helps); you also need to be careful about
> losing core electrons from the Fe. In both cases look in case.outputm
> to see how far the core integrals are from integers. Scale RKMAX so
> RKMAX/min(RMT) is roughly the same (e.g. 3.5), although you need to
> add a bit when you decrease the RMTs. Probably something like 5-6
> should be good for your problem.
>
> How to chose the "right" RMTs? I don't have any great wisdom, others
> might have. I tend to use RMTCheck (look in the mailing list, or I can
> ask Peter to add it to the contributed software) and check that the
> step in the gradients at the RMT for the different atoms are
> comparable. In most cases this gives results similar to setrmt. In
> principle you can also do calculations for different values with
> RKMAX/min(RMT) fixed and look for the minimum energy -- the few times
> I've done this the results are about the same. Another method would be
> to try and balance the charge lost in the core integrals, which gives
> a similar result.
>
> 2011/4/21 Maxim Rakitin <rms85 at physics.susu.ac.ru>:
> > Thank you Evgenia,
> >
> > I've already seen that link, but I'd like to get information why it is
> not
> > possible from physical point of view.
> >
> > Maxim
> >
> > 21.04.2011 16:53, Евгения Каблиман пишет:
> >
> > Dear Maxim,
> >
> > identical elements should have identical RMT's.
> > This link might help you http://www.wien2k.at/reg_user/faq/rmt.html .
> >
> > 2011/4/21 Maxim Rakitin <rms85 at physics.susu.ac.ru>
> >>
> >> Dear WIEN2k community,
> >>
> >> Is it correct to perform calculations with different Rmt radii for atoms
> >> of one type, e.g. Fe?
> >>
> >> I need to calculate total energy of a systems containing one
> interstitial
> >> carbon atom in bcc iron matrix. Carbon has quite large MT-radius
> comparing
> >> with H atom, so StructGen sets Rmt(Fe) to 1.59 a.u. and Rmt(C) to 1.41
> a.u.
> >> for lattice constant 5.394 a.u. In some papers (C. Domain et al., PRB
> 69,
> >> 144112 (2004)) Rmt(C) is even large than I got (~1.6 a.u.) and Rmt(Fe)
> is
> >> also much larger (~2.4 a.u.). But if I use the radii from the article,
> >> WIEN2k doesn't allow me to perform further procedures - nn gives me
> >> information about overlapping spheres.
> >>
> >> Can I use Rmt(Fe)=2.4 a.u. in all volume of my supercell except of the
> >> nearest iron atoms?
> >>
> >> Thanks in advance for your answers.
> >>
> >> --
> >> Best regards,
> >>   Maxim Rakitin
> >>   South Ural State University
> >>   Chelyabinsk, Russia
> >>   email: rms85 at physics.susu.ac.ru
> >>   web: http://www.susu.ac.ru
> >>
> >> _______________________________________________
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> >> Wien at zeus.theochem.tuwien.ac.at
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> >
> >
> >
> > --
> > Evgeniya Kabliman.
> > Insitute of Materials Chemistry         Vienna University of Technology
> > Getreidemarkt 9/165-TC, A-1060 Vienna, Austria
> > Tel: +43 1 58801 15674        Fax: +43 1 58801 15698
> > evgeniya at theochem.tuwien.ac.at            http://www.imc.tuwien.ac.at
> >
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> >
>
>
>
> --
> Laurence Marks
> Department of Materials Science and Engineering
> MSE Rm 2036 Cook Hall
> 2220 N Campus Drive
> Northwestern University
> Evanston, IL 60208, USA
> Tel: (847) 491-3996 Fax: (847) 491-7820
> email: L-marks at northwestern dot edu
> Web: www.numis.northwestern.edu
> Chair, Commission on Electron Crystallography of IUCR
> www.numis.northwestern.edu/
> Research is to see what everybody else has seen, and to think what
> nobody else has thought
> Albert Szent-Gyorgi
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-- 
Evgeniya Kabliman.
Insitute of Materials Chemistry         Vienna University of Technology
Getreidemarkt 9/165-TC, A-1060 Vienna, Austria
Tel: +43 1 58801 15674        Fax: +43 1 58801 15698
evgeniya at theochem.tuwien.ac.at            http://www.imc.tuwien.ac.at
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